Editor's Note:​ With the widespread adoption of battery-powered applications such as portable devices, AGVs (Automated Guided Vehicles), medical instruments, and consumer robots, stepper motors face a critical challenge: how to balance positioning accuracy with battery life under limited power supply. Traditional constant high-current driving methods not only waste substantial energy in the form of heat but also accelerate battery depletion and can even compromise system reliability due to overheating. Therefore, systematically reducing the power consumption of stepper motors has become a key factor in extending device runtime and improving user experience.


Stepper motors are widely used for their simple open-loop control and low cost, but they have a well-known drawback—high energy consumption and significant heat generation. Conventional driving methods often apply a constant high current to the motor regardless of load conditions, wasting energy as heat. This article explores how to systematically achieve low-power operation of stepper motors from two dimensions—control strategies and hardware optimization—in light of recent technological trends.


1. Load-Based Closed-Loop Control: Current "On Demand"

Traditional open-loop drives use a fixed current to drive the motor. To ensure no step loss, this current is often much higher than actually required. The core idea for achieving low power consumption is to introduce closed-loop control that dynamically adjusts the current based on real-time load conditions.

New-generation closed-loop stepper drivers use encoder feedback to sense rotor position and detect load changes in real time. When light load or no load is detected, the driver automatically reduces the winding current; when the load increases, it raises the current to provide sufficient torque. For example, Toshiba’s TB67S579FTG incorporates "Second-Generation Active Gain Control (AGC2)," which determines the load by sensing the motor’s back EMF voltage and automatically adjusts the drive current to the minimum necessary level, thereby significantly improving efficiency.

Furthermore, closed-loop algorithms based on Field-Oriented Control (FOC) enable finer current regulation. Compared with traditional open-loop modes, FOC can increase torque output by 1.5 to 2 times at the same current, or substantially reduce current demand for the same torque, thus cutting energy consumption at its source.


2. Half-Current Lock: "Energy-Saving Sleep" at Standstill

When a stepper motor stops rotating but remains locked, maintaining the rated current causes significant heating and wastes electricity. "Half-current lock" is a classic and effective solution to this problem.

This function automatically reduces the winding current to half of the set value after the motor stops receiving pulse signals (e.g., after 0.5 seconds without step pulses). Although the output torque decreases accordingly, it is usually sufficient for holding applications. When new pulses arrive, the current instantly returns to the rated value, ensuring normal motion without interruption. Many drivers (such as Beijing Hollysys SH-20403 and the AT2100 chip) already include automatic half-current lock as a standard feature.


3. Dual-Voltage Drive and Constant-Voltage Drive Optimization

The choice of drive voltage directly affects both power consumption and high-speed performance.

A dual-voltage drive strategy effectively balances low-speed and high-speed performance: at low speeds, a lower voltage (UL) is applied to avoid excessive current and heating; when high-speed operation is needed, a higher voltage (UH) is switched in to overcome winding inductance and maintain high torque output. This approach combines low-speed energy efficiency with high-speed dynamic response and represents a hardware-level optimization.

For systems using constant-voltage drive, the on-resistance (RDS(on)) of MOSFET power devices is the main source of loss. Selecting an H-bridge driver with low on-resistance directly reduces power dissipation. For instance, SGMICRO’s SGM42618 features a total output-stage on-resistance of only 0.4 Ω (high-side + low-side), significantly lowering thermal losses.


4. H-Bridge Optimization: Improving Driver-Stage Efficiency

The H-bridge is the power output stage of a stepper motor driver, and its efficiency directly impacts overall power consumption.

Modern drivers incorporate several optimizations in H-bridge design:

  • Low-impedance power devices: Using MOSFETs with lower on-resistance reduces voltage drop and heating during current flow.
  • Integrated PWM current control and synchronous rectification: Internal PWM circuitry precisely controls winding current, avoiding energy waste. Synchronous rectification allows MOSFETs to conduct via low-resistance paths during current decay, further reducing losses.
  • Optimized decay modes: Adaptive decay technology automatically selects the optimal decay mode (fast, slow, or mixed) based on motor parameters, minimizing unnecessary energy consumption during current regulation while ensuring smooth operation. Delay-matching design in the H-bridge also improves switching losses between high-side and low-side transistors.


Summary

Achieving low-power operation of stepper motors requires a systematic "combination punch" of optimizations:

  • Core strategy: Adopt load-based closed-loop dynamic current adjustment so that energy consumption follows actual demand—this is the most critical innovation.
  • Basic function: Enable half-current lock to eliminate wasteful consumption during standstill locking.
  • Hardware selection: Choose modern driver chips with low-impedance H-bridges, support for dual-voltage switching, or intelligent current regulation capabilities (e.g., SGM42618, TB67S579FTG, etc.).